The Outer Reaches 2

This page uses the concept of Hubble Volumes to think about infinite three-dimensional space.

Hubble Volumes - Infinite Space

Hubble Volumes

Locating universes in the Allspace would probably require a Hubble-sized leap in technology. I use the phrase Hubble-sized leap here much in the way one might use quantum-leap, yet I also want to recall that Edwin Hubble was the first to verify other galaxies in 1923 and his name is given to the Hubble Space Telescope launched in 1990. Moreover, the term Hubble volume (or Hubble sphere) refers to the outer limit of the light we can see; past this limit, light recedes from an observer (because of the expansion of the universe) at a rate that’s greater than the speed of that light moving toward the observer (and hence it can’t be seen).

Hubble volume is sometimes confused with our known universe, yet our Hubble volume is smaller than our known universe. The term is a measure of how much light an observer is able to see — which could apply anywhere in our universe or in any universe containing light (or related waves and/or particles such as electromagnetic radiation or cosmic rays from supernovae). The definite article is important here: astronomers talk of a Hubble volume, not the Hubble volume.

It may be that universes are moving away from each other faster than the speed of light and we may therefore never see a universe different than our own. Or, perhaps some day we will detect a frequency or particle that travels faster than light, and the structure of universe clusters will be revealed to us, just as the stars in Andromeda were revealed to Edwin Hubble.

Cropped NASA image of MACS0647-JD, which “is a candidate for the farthest known galaxy from Earth and is at redshift of about z=10.7 or 13.3 billion light-years (4 billion parsecs) away. It formed 420 million years after the Big Bang. It is less than 600 light-years wide” (“MACS0647-JD," Wikipedia).

While I speculate that other universes exist in the same space-time continuum as ours, I suspect that these universes are so far away that they don’t necessarily share the things we take for granted in this corner of our galaxy. Our understanding of our own universe is just beginning — it’s barely a hundred years old, and I’m not sure we can yet make assumptions about the uniformity, basic properties, or constants of the far-off galaxies that we can presently detect. I think it would be premature to assume anything specific about universes we haven’t even detected yet.

A Hubble volume gives us a type of measure — approximate, inexact — of the size of other universes we may yet find. Just as stars, solar systems, and galaxies come in different sizes, so other universes are likely to differ in size, yet we may assume (at least for the present purposes) that they’re likely to be of a similar magnitude. Finally, the notion of a Hubble volume is helpful in that it reminds us that what we see is dependent on where we see it from. And, of course, the way we interpret what we see.

My position regarding other universes is even more precarious than that of the 9th century astronomer al-Sufi, who called Andromeda a small cloud, and who would need to have lived another thousand years to fully understand that what he saw was in fact a far-off galaxy. We may have already seen some tiny dot or cloud of light — some blip, pulse, particle, or wave — that in a hundred or a thousand years we’ll know comes from a universe sextillions of gigaparsecs from Earth.

Yet on the other hand, we may never, ever see anything like al-Sufi’s little cloud. Perhaps even in a million years, and from the perspectives of a billion alien life forms, such a thing will never be seen. The wonderful thing about practical space, however, is that this doesn’t mean another universe doesn’t exist. Unless, of course, we reach an absolute end of space; unless we can verify that it curves in upon itself and that what we can verify is the totality of three-dimensional existence.

While universe clusters have no data to back them up, they nevertheless derive from two reasonable expectations, two practical extrapolations.

First, in every sphere, be it physical or intellectual — we find that there’s always something outside or beyond that sphere. In thought as in space. Whatever we see or imagine, we can see or imagine something beyond that. This practical view of space can be questioned but not disproven either practically or theoretically. Given that we don’t understand the composition or nature of our universe, why would we assume that outer space be any different than the most fundamental aspect of the space in front of us?

Second, why would we assume that the historical precedence of continued expansion would stop precisely at the limit of our present detection? Before astronomy proved otherwise, astronomers believed that the earth didn’t move and that some of the heavenly bodies performed odd little ellipses, which helped astronomers to make sense of otherwise inexplicable data. The moon was a goddess or a friend Li Bai hoped to meet one day among the Milky infinity of stars. The sun was a god in his chariot, or the sun filtered down from God, from the wings of the holy dove. Before astronomy proved otherwise, we imagined our galaxy so vast that it could stand in for any practical notion of infinity.

To discount the possibility of universe clusters may be to think in the same way we thought prior to Edwin Hubble and the 1920s, back when this galaxy seemed so vast that it simply had to be everything there was: The Milky Way, Via Lactea, Galaxías Kýklos, astronomical Goddess of Absolute Space. Hubble showed us that our galaxy wasn’t all there was to space, not in a million years. Today we see that our 100-400 billion stars need to be multiplied by hundreds of billions of galaxies to get a sense of the way our universe is populated by stars. This may be the tip of the iceberg; our universe may be an infinitesimal fraction of total space. Why would our universe be any different — any more absolute a framework — than the Milky Way?

Infinite Space

The astronomer is like the physicist, who looks inward to quarks and bosons, and thus appears to deal with infinite depths. Yet the astronomer’s near-infinite depths are more certain. Zeno’s paradox (in which small spaces divide infinitely and as a result you can never go from point A to point B) works mathematically but is also something of a logical trick or reductio ad absurdum (reduction to absurdity): no matter how many times you divide a millimetre, it remains a millimetre and can be set beside other millimetres; you can, despite Zeno’s theoretical argument, get from point A to point B. The infinity of outer space, on the other hand, doesn’t have the same type of practical objections.

The same sort of practical objection applies to arguments about multiple dimensions or alternative spatial universes. Imagine that one hundred and fifty students are sitting in an auditorium, listening to a theorist question the overwhelming importance of the traditional space-time continuum. The theorist says, “We’re limited by our own three and four dimensional concepts. In truth, we’re living multiple versions of ourselves. Every moment is configured in an infinity of universes or dimensions.” This is a fascinating exercise in thought, and it may well find correlates in math or physics. Yet students who believe they're actually existing at that moment in another dimension or space-time continuum are either 1) schizophrenic, 2) wishing to God they were somewhere else (and are managing to make a momentary psychological break), or 3) in fact simultaneously in another dimension. In all three cases, they've no proof that they’re in another continuum or dimension — or, at least, no proof other than the claim of experience, which puts them in the company of those who talk about Jesus or nirvana. Yet these same students will soon be given undeniable proof of the continuum in which they do exist: when the bell rings they'll be required to lift their undeniable bodies from their undeniable seats and leave the undeniable room.

There may be dimensions outside the auditorium, yet the only one we know for sure has halls and exits, roads and oceans, a pinprick called Earth and an infinity of directions into the universe. If theorists suggest that we’re limited by this conception, then I suggest they re-consider where exactly this limit lies.

Outer space isn’t like inner space: while we can theorize an infinity of spaces or sub-degrees within any given arc, in practice one space ends and the next begins. Yet when we project outward from Earth, the minutes of an arc become seconds, the seconds become deciseconds, centiseconds, milliseconds, picoseconds, nanoseconds, etcetera — and, I would argue, ad infinitum. Inner space seems infinitely complex yet it has practical limits, whereas outer space is infinitely complex and has no practical limits. The space of astrophysics has the same infinite divisibility as the space of subatomic physics, yet the former becomes increasingly hard to measure yet just as likely as ever, while the latter becomes increasingly hard to measure and then disappears.

Of course, the notion of infinitely small space opens all sorts of interesting avenues — from extreme nonotechnology to science-fictional notions of alien operations at a subatomic level (which appear to humans as invisible operations or magic). I use this latter idea as the basis of my science fiction novel, The Pulse, much in the way science-fictions writers use worm holes to overcome the problem of transportation across vast distances. Yet these types of extrapolations remain highly theoretical, more akin to fiction than the world as we know it. The notion of infinite astronomical space, on the other hand, is increasingly being verified by astronomers and has no practical objection.